Step Families Support Group
Traditionally, a stepfamily is the family one acquires when a parent enters a new marriage, whether the parent was widowed or divorced. This community is focused on many of the relationships and issues that may arise within stepfamilies where you may find answers from some members and you may help other members with their questions.
He needs to get a routine/pattern down. When he demands attention, teach him when someone else is talking, he needs to wait until they get done....no interupting type of thing.
Since he is 3, he may not understand as much when you "talk" to him.....try showing more action and eventually he will trust more.
This will take time, but he will learn to trust.